1. Field of the Invention
Systems and methods consistent with the principles of the invention relate generally to data communication and, more particularly, to data communication within cable modem systems.
2. Description of Related Art
In cable modem systems, a cable modem termination system (CMTS) at one end of a cable network typically services multiple cable modems (CMs) connected to the cable network. CMs are generally installed locally at the end-user's location, and communicate with the CMTS, which may be installed at a cable company's facility. The CMTS transmits data and messages to the CMs in a “downstream” direction and receives data bursts from the CMs in an “upstream” direction.
Data over Cable Service Interface Specification (DOCSIS) is a commonly used communications protocol that defines interface requirements for CMs. DOCSIS 2.0, for example, builds upon the capabilities of DOCSIS 1.0 and DOCSIS 1.1 and adds throughput in the upstream portion of the cable system. This increased upstream data capacity enables symmetrical and time-critical services such as videoconferencing and peer-to-peer applications. When sharing a communication channel with a CMTS, the CMs may use modulation schemes in which the modems transmit data bursts to the CMTS during designated time intervals.
CMTSs typically receive data though a number of physical ports and further distinguish between different frequencies or “channels” of data using a number of internal receivers. Current CMTSs typically have a fixed relationship between their internal receivers and the physical ports.
Certain data communication, such as voice over Internet protocol (VoIP), may require data blocks to be transmitted on an upstream channel on a periodic basis, such as once in every 10 ms, 20 ms, or 30 ms time interval. The same time period may be allocated to the data communication within each time interval. It is important to use each upstream channel as fully as possible. Therefore, data blocks from different data communications may be packed together as much as possible.
CM initialization requires that certain information be communicated from the CMs to the CMTS on the upstream channels. As a result, CM initialization requires a lot of bandwidth, thereby limiting the amount of data communication that can occur on the upstream channels.
CM initialization includes two characteristics: initial maintenance and registration. For initial maintenance, the CMTS allocates a certain portion of every time interval for initialization of CMs. For example, the CMTS allocates 1.6 ms within each 10 ms time interval for initialization of a CM. During registration, a CM transmits a large packet (e.g., 1500 byte registration packet) to the CMTS. The packet must be transmitted without any disturbances and cannot be fragmented.
CM initialization may not occur during every time interval. The CMTS, nevertheless, must allocate a portion of each time interval for CM initialization. For example, a 1.6 ms period of each time interval may be dedicated to CM initialization, leaving an 8.4 ms period for other data communication. When the 1.6 ms period is not used for CM initialization, then this period is wasted, leading to an inefficient use of upstream channel bandwidth.
Accordingly, there is a need to more efficiently use upstream channel bandwidth in cable modem systems.